Synthesis of zeolites of faujasite structure

ABSTRACT

A process is provided for the preparation of zeolites belonging to the faujasite structural class and exhibiting a Si:Al ratio higher than 1 in which a reaction mixture is first produced which has a pH higher than 10 and contains water, a source of tetravalent silicon, a source of trivalent aluminum, a source of hydroxide ions in the form of a strong inorganic or orgnaic base and a structuring agent ST so as to produce an aluminosilicate gel having the desired composition to permit its crystallization into a compound of the faujasite structural class. The gel obtained is kept at a temperature, pressure and for a sufficient period to effect the crystallization of the gel into a precursor of the zeolite consisting of the zeolite trapping the structuring agent ST in its cavities and the precursor is then subjected to a calcination to destroy the structuring agent and to produce the zeolite. The structuring agent ST consists of at least one compound belonging to the group formed by the carbon-containing macrorings and macropolyrings which contain in the rings, heteroatoms chosen from oxygen, nitrogen, silicon and sulphur, and which contain 10 to 24 atoms per ring. Precursors of the zeolites are also provided.

BACKGROUND OF THE INVENTION

The invention relates to a process for the synthesis of zeolitesbelonging to the faujasite structural group. It further relates to theproducts obtained and to their application in adsorption and catalysis.

DESCRIPTION OF THE RELATED ART

Zeolites are crystalline tectosilicates. The structures consist ofassemblies of TO₄ tetrahedra forming a three-dimensional skeleton bysharing oxygen atoms. In zeolites of the aluminosilicate type which arethe most common ones, T denotes tetravalent silicon and trivalentaluminium. The abovementioned three-dimensional skeleton exhibitscavities and channels which have molecular dimensions and accommodatecations compensating the charge deficiency linked with the presence oftrivalent aluminium in the TO₄ tetrahedra, the said cations beinggenerally exchangeable.

As a general rule, the composition of zeolites may be denoted by theempirical formula (M₂ /_(n) O; Y₂ O₃ ; x ZO₂) in the dehydrated andcalcined state. In this formula Z and Y denote the tetravalent andtrivalent elements of the TO₄ tetrahedra respectively, M denotes anelectropositive element of valency n, such as an alkali oralkaline-earth metal and constitutes the compensating cation, and x is anumber which can vary from 2 to theoretically infinity, in which casethe zeolite is a silica.

Each type of zeolite has a distinct microporous structure. The variationin the dimensions and shapes of the micropores from one type to anotherresults in changes in the adsorbent properties. Only molecules whichhave certain dimensions and shapes are capable of entering the pores ofa particular zeolite.

Because of these remarkable characteristics, zeolites are veryparticularly suitable for the purification or separation of gaseous orliquid mixtures, such as, for example, the separation of hydrocarbons byselective adsorption.

The chemical composition, including in particular the nature of theelements present in the TO₄ tetrahedra and the nature of theexchangeable compensating cations, is also an important factor involvedin the selectivity of the adsorption, and above all in the catalyticproperties of these products. They are employed as catalysts or catalystsupports in the cracking, reforming and modification of hydrocarbons,and in the conversion of many molecules.

Many zeolites exist in nature; they are aluminosilicates whoseavailabilities and properties do not always correspond to therequirements of industrial applications. Consequently, the search forproducts which have new properties has led to the synthesis of a largevariety of zeolites, essentially of the aluminosilicate type. Among themany examples of this type there may be mentioned zeolite A (U.S. Pat.No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S.Pat. No. 3,130,007), zeolite L (FR-A-1,224,154), zeolite T(FR-A-1,223,775), zeolite ZSM5 (U.S. Pat. No. 3,702,886), zeolite ZSM 12(U.S. Pat. No. 3,832,449) and zeolite ZSM 48 (EP-A-0,015,132).

Zeolites of the faujasite structural group are characterized by athree-dimensional framework structure which can be described by means ofthe assembly of modules called cube-octahedra. Each of these modulesconsist of 24 tetrahedra containing the elements Si and Al and bridgedby oxygen according to the principle described above. In thecube-octahedron the tetrahedra are linked so as to form eight ringscontaining six tetrahedra and six rings containing four tetrahedra. Eachcube-octahedron is joined with tetrahedral coordination, via four ringscontaining six tetrahedra, to four neighbouring cube-octahedra.

To show the relationships which unite the various members of thestructural group it is convenient to consider the structural planes inwhich the cube-octahedra are arranged at the vertices of a plane networkof hexagons. Each cube-octahedron is thus connected to three neighboursin the structural plane.

The fourth connecting direction is directed alternately on each side ofthe structural plane and enables the cube-octahedra to be connectedbetween neighbouring and parallel structural planes.

According to the mutual relative arrangement of these structural planes,it is possible to obtain

sequences of three distinct structural planes ABCABC . . . correspondingto a structure of cubic symmetry,

sequences of two distinct structural planes ABAB . . . corresponding toa structure of hexagonal symmetry,

more complex sequences, which may be regular or irregular.

All the solids belonging to the faujasite structural group are polytypesand have interconnected channels approximately 0.8 nm is diameter. Thus,faujasite is a natural zeolite whose structure corresponds to thestacking of three distinct structural planes ABC corresponding to astructure of cubic symmetry. Compounds with the same structure asfaujasite can be obtained by synthesis from a sodium aluminosilicategel, the said compounds being called zeolites X when the Si:Al ratio ofthe number of atoms of silicon to the number of atoms of aluminium isbetween 1 and 1.5, and zeolites Y when the said Si:Al ratio is between1.5 and 3. Si:Al ratios higher than 3 cannot be obtained by synthesis.

Nevertheless, there exist postsynthesis treatments which make itpossible to raise the value of the Si:Al ratio above 3, for example ahigh-temperature steam treatment after the Na⁺ cations have beenexchanged for protons or lanthanum cations. Certain properties can thusbe improved, such as the hydrothermal stability needed in certainapplications like, for example, the cracking of hydrocarbon molecules inpetroleum refining.

Compounds whose structure approaches the hexagonal structure ABABAB . .. can also be obtained by synthesis, but with stacking defects, whichare seen as the broadening of some lines in the x-ray diffractionpatterns employed to identify these compounds. Thus, zeolite ZSM-3 (U.S.Pat. No. 3,415,736) is prepared in a medium containing Na⁺ and Li⁺cations; its Si:Al ratio is close to 1.5. By employing the Cs⁺ and Na⁺cation pair, zeolite CSZ-3 (U.S. Pat. No. 4,333,859) is obtained, whoseSi:Al ratio is close to 3. Zeolites of the type ZSM 20 (U.S. Pat. No.3,972,983) crystallize in the presence of tetraethylammonium cations(TEA⁺) associated with Na⁺ cations; however, to obtain the maximum Si:Alratio of 4.4, an aluminosilicate gel which has a Si:Al ratio close to 15and a TEA⁺ :Si molar ratio close to 1 must be employed.

The general process of synthesis of zeolites of the faujasite structuralgroup consists of a hydrothermal crystallization of aluminosilicate gelsof particular compositions containing a structuring agent, which may bea metal cation and optionally an organic cation or compound such asTEA⁺.

More precisely, a process of this kind consists in producing first ofall a reaction mixture which has a pH higher than 10 and contains water,a source of tetravalent silicon, a source of trivalent aluminium, asource of hydroxide ions in the form of a strong inorganic or organicbase, optionally a source of M^(n+) metal cations, n being the valencyof M, and optionally a structuring agent ST so as to obtain analuminosilicate gel which has the desired composition to permit itscrystallization into a compound of the faujasite structural group, andin then maintaining the gel obtained, directly or after prior maturing,at a temperature not exceeding 150° C. and under a pressure which is atleast equal to the autogenous pressure of the mixture consisting of thesaid gel for a sufficient period to effect the crystallization of thisgel.

When the structuring agent is an organic compound such as TEA⁺, theproduct resulting from the crystallization, after washing with distilledor deionized water and drying below 100° C., is a precursor of therequired zeolite, which consists of the said zeolite trapping thestructuring agent in its cavities. The change from the precursor to thecorresponding zeolite is made by subjecting the said precursor to acalcination at a temperature which is suitable for destroying theorganic structuring agent.

As indicated earlier, a process of this kind does not make it possibleto synthesize zeolites which have the faujasite structure of cubicsymmetry and a Si:Al ratio higher than 3. Moreover, in the case of thesynthesis of hexagonal polytype zeolites of faujasite, obtaining a Si:Alratio higher than 3 requires the use of an aluminosilicate gelexhibiting a high Si:Al ratio and simultaneously containing a molarquantity of structuring agent, for example TEA⁺ cations, which is closeto the molar quantity of silica employed to form the initial reactionmixture, that is to say substantially higher than the molar quantity ofthe aluminium element.

SUMMARY OF THE INVENTION

It has now been found that certain organic molecules belonging to theclass of carbon-containing macrorings and macropolyrings containingheteroatoms chosen from oxygen, nitrogen, silicon and sulphur, have theproperty of directing the crystallization of aluminosilicate gelstowards zeolites of the faujasite structural group, which arecharacterized by a high Si:Al ratio, generally higher than 3. Dependingon the size and the symmetry of the macroring or macropolyring, it ispossible to obtain either a zeolite exhibiting a cubic structure or azeolite exhibiting a hexagonal structure. It is also possible to obtaina zeolite of faujasite type, made up of variable proportions of thesetwo types of structure by employing mixtures of the said molecules ofthe abovementioned type with each other or with oxygen-containingacyclic costructurants. The use of the said costructurants mixed withsome of the molecules of the abovementioned type also makes it possibleto form zeolites of the faujasite type with cubic structure.Furthermore, the macroring or macropolyring introduces a pronouncedstabilizing effect, which makes it possible to decrease theconcentration of the hydroxide ions in the synthesis medium, whichresults in obtaining a high Si:Al ratio and a substantial improvement inthe yield, the said stabilizing effect still being maintained in thepresence of the oxygen-containing acyclic costructurant. Thus, the Si:Alratio of the initial gel may be very close to the final Si:Al ratio inthe zeolite crystals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The subject of the invention is therefore a process for the preparationof zeolites belonging to the faujasite structural class and exhibiting aSi:Al ratio higher than 1 and capable of exceeding 3, the said processbeing of the type in which a reaction mixture is produced first of all,which has a pH higher than 10 and contains water, a source oftetravalent silicon, a source of trivalent aluminium, a source ofhydroxide ions in the form of a strong inorganic or organic base and astructuring agent ST so as to obtain an aluminosilicate gel having thedesired composition to permit its crystallization into a compound of thefaujasite structural class. The gel obtained is then maintained,optionally after prior maturing, at a temperature not exceeding 150° C.and at a pressure at least equal to the autogenous pressure of themixture consisting of the said gel for a sufficient period to effect thecrystallization of this gel into a precursor of the zeolite consistingof the zeolite trapping the structuring agent ST in its cavities. Thesaid precursor is subjected to a calcination to destroy the structuringagent and to produce the zeolite, and it is characterized in that thestructuring agent ST consists of at least one compound MC belonging tothe group formed by the carbon-containing macrorings and macropolyringswhich contain in the ring(s) heteroatoms chosen from oxygen, nitrogen,silicon and sulphur and which contain 10 to 24 atoms per ring.

The quantity of structuring agent ST present in the reaction mixtureintended to form the gel is advantageously such as to make the molarratio ST:Al^(III) range from 0.1 to 4, the said ratio preferably rangingfrom 0.1 to 1 and very particularly from 0.2 to 0.5.

In particular, the ingredients making up the reaction mixture givingrise to the aluminosilicate gel are employed so that the said gel mayhave, in terms of molar ratios, the following composition,

    ______________________________________                                                    Advantageous                                                                            Preferred                                                           ranges    ranges                                                  ______________________________________                                        Si.sup.IV :Al.sup.III                                                                         2 to 20   4 to 10                                             OH.sup.- : Al.sup.III                                                                       0.5 to 8    1 to 6                                              ST:Al.sup.III 0.1 to 4    0.1 to 1                                            H.sub.2 O:Al.sup.III                                                                          40 to 200 50 to 150                                           ______________________________________                                    

The MC compounds which can be employed to form the structuring agent STin the process according to the invention may be especially:

crown ethers whose ring contains 10 to 24 atoms and comprises solelyoxygen atoms as heteroatoms, at least 4 in number, among which thefollowing compounds may be mentioned:

1,4,7,10-tetraoxacyclododecane(12-crown-4 ether),

1,4,7,10,13-pentaoxacyclopentadecane(15-crown-5 ether),

1,4,7,10,13,16-hexaoxacyclooctadecane(18-crown-6-ether),

2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadecane(dibenzo-18-crown-6 ether),

2,3,11,12-dicyclohexano-1,4,7,10,13,16-hexaoxacyclooctadecane(dicyclohexano-18-crown-6 ether),

2,3,14,15-dibenzo-1,4,7,10,13,16,19,22-octaoxacyclotetracosane(dibenzo-24-crown-8ether),

2,3,14,15-dicyclohexano-1,4,7,10,13,16,19,22-octaoxacyclotetracosane(dicyclohexano-24-crown-8ether),

2,3-benzo-1,4,7,10,13-pentaoxacyclopentadecane(benzo-15-crown-5 ether);

compounds which have a structure comparable to that of the above crownethers but in which the oxygen atoms in the ring are partially orcompletely replaced by substituents chosen from sulphur atoms and thegroups >NH, >NR and >SI<_(R) ^(R) in which R is a C₁ -C₄ hydrocarbyl,among which there may be mentioned the following compounds:

1,4,8,11-tetraazacyclotetradecane,

1,4,8,12-tetraazacyclopentadecane,

1,4,8,11-tetraazacyclotridecane,

1,4,7,10,13,16-hexaazacyclooctadecane trisulphate (hexacyclenetrisulphate),

14-(1,1-dimethylsila)-1,4,7,10,13-pentaoxacyclotetradecane(dimethylsila-14-crown-5 ether),

11-(1,1-dimethylsila)-1,4,7,10-tetraoxacycloundecane(dimethylsila-11-crown-4 ether) and its 3,6,9-methyl derivative,

17-(1,1-dimethylsila)-1,4,7,10,13,16-hexaoxacycloheptadecane(dimethylsila-17-crown-6 ether),

20-(1,1-dimethylsila)-1,4,7,10,13,16,19-heptaoxacycloeicosane(dimethylsila-20-crown-7 ether),

1,4,7,10,13,16-hexathiacyclooctadecane,

17-(1-methyl-1-vinylsila)-1,4,7,10,13,16-hexaoxacycloheptadecane(methylvinylsila-17-crown-6 ether),

14-(1-methyl-1-vinylsila)-1,4,7,10,13-pentaoxacyclotetradecane(methylvinylsila-14-crown-5 ether),

1,7,10,16-tetraoxa-4,13-diazacyclooctadecane (Kryptofix 22),

1,7,10-trioxa-4,13-diazacyclopentadecane (Kryptofix 2.1);

carbon-containing macropolyrings of the type ofpolyoxadiazabicycloalkanes in which each ring contains 10 to 18 atomsand has at least two oxygen atoms in addition to the two nitrogen atoms,among which there may be mentioned the following compounds:

4,7,13,16,21-pentaoxa-1,10-diazabicyclo[8.8.5]tricosane (Kryptofix2.2.1),

4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (Kryptofix2.2.2).

The use of a structuring agent ST₂ consisting of at least one compoundMC₂ chosen from the macrorings according to the invention whose ringcontains at least 18 atoms, for example1,4,7,10,13,16-hexaoxacyclooctadecane,1,7,10,16-tetraoxa-4,13-diazacyclooctadecane, hexacyclene trisulphate or1,4,7,10,13,16-hexathiacyclooctadecane, results in the formation ofzeolites which have the hexagonal symmetry structure of the hexagonalpolytypes of faujasite.

The use of a structuring agent ST₁ consisting of at least one compoundMC₁ chosen from the macrorings according to the invention which havefrom 10 to 17 atoms in the ring and the macropolyrings according to theinvention which have a number of atoms ranging from 10 to 18 in eachring, for example 1,4,7,10,13-pentaoxacyclopentadecane,4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane or17-(1,1-dimethylsila)-1,4,7,10,13,16-hexaoxacycloheptadecane, produceszeolites which have the faujasite structure of cubic symmetry.

When employing a structuring agent ST consisting of a mixture of atleast one compound MC₁ with at least one compound MC₂, zeolites of thefaujasite type are obtained, which are products made up of domains whichhave the structure of a cubic faujasite and of domains which have thestructure of a hexagonal faujasite.

To characterize these products, a coefficient α may be defined, denotingthe fraction of phase of the faujasite type with a structure ofhexagonal symmetry in the product, the said coefficient α being suchthat α=1 for a product consisting solely of a faujasite with a structureof hexagonal symmetry and that α=0 for a product consisting solely of afaujasite with a structure of cubic symmetry.

In an alternative form of the process according to the invention, thestructuring agent ST results from the association of at least onecompound MC defined earlier and therefore including the compounds MC₁and MC₂ with a costructurant CS consisting of at least oneoxygen-containing acyclic compound chosen from the compounds of formula

    R.sub.1 --O--C.sub.m H.sub.2m-1 X--O].sub.8 R.sub.2

in which each of R₁ and R₂, which are identical or different, denotes ahydrogen atom or a C₁ -C₄ alkyl radical, X denotes a hydrogen atom or an--OH radical, m is equal to 2 or 3 and may be different from one repeatunit to another and g is a number ranging from 1 to 12.

Examples of compounds of abovementioned formula which may be employed toform the costructurant are such as ethylene glycol methyl ether offormula CH₃ OCH₂ CH₂ OH, ethylene glycol dimethyl ether of formula CH₃OCH₂ CH₂ OCH₃, ethylene glycol of formula HOCH₂ CH₂ OH, propylene glycolof formula HOCH₂ CH₂ CH₂ OH, methyl ethers of polyethylene glycols offormula CH₃ --O--CH₂ CH₂ O]_(g).sbsb.1 H and polyethylene glycols offormula OH--CH₂ CH₂ O]_(g).sbsb.1 H with g₁ ranging from 2 to 9, andespecially tetraethylene glycol, pentaethylene glycol, hexaethyleneglycol, heptaethylene glycol, octaethylene glycol and mixtures of suchglycols, polypropylene glycols of formula HO--CH₂ CH₂ CH₂ O]_(g).sbsb.1H with g₁ ranging from 2 to 9, and especially tripropylene glycol andtetrapropylene glycol.

The quantity of structuring agent resulting from the association of atleast one compound MC with the costructurant CS, which is present in thereaction mixture intended to form the gel and the composition of thesaid structuring agent are such as to make the molar ratio structuringagent:Al^(III) range from 0.1 to 4 and so as to make the molar ratioMC:Al^(III) equal to or higher than 0.05. The said quantity andcomposition are preferably such as to make the molar ratio structuringagent: Al^(III) range from 0.2 to 2 and to make the molar ratioMC:Al^(III) equal to or higher than 0.1.

The costructurant CS defined above directs the crystallization of thealuminosilicate gels towards zeolites of the faujasite type with astructure of cubic symmetry. A structuring agent ST₃ associating thecostructurant CS and at least one compound MC₁ results in the formationof zeolites of faujasite type with a structure of cubic symmetry. Astructuring agent associating the costructurant CS and at least onecompound MC₂ results in the formation of products made up of domainswhich have the structure of a cubic faujasite and of domains which havethe structure of a hexagonal faujasite. Similarly, by associating astructuring agent ST₃ with at least one compound MC₂, products made upof domains of the above-mentioned two types are also obtained.

Among the sources of tetravalent silicon Si^(IV) which can be employedin the preparation of the reaction mixture intended to form thealuminosilicate gel there may be mentioned finely divided solid silicasin the form of hydrogels, aerogels or colloidal suspensions,water-soluble silicates such as alkali metal silicates like sodiumsilicate, and hydrolysable silicic esters such as tetraalkylorthosilicates of formula Si(OR)₄ in which R denotes a C₁ -C₄ alkyl suchas methyl and ethyl. The source of silicon is used in the form of a trueaqueous solution, in the case of water-soluble silicates, or else of anaqueous suspension which may be colloidal, in the case of finely dividedsilicas.

Suitable sources of trivalent aluminium Al^(III) are aluminium saltssuch as aluminium sulphate, nitrate, chloride, fluoride, acetate,aluminium oxides and hydroxyoxides, aluminates and especially alkalimetal aluminates such as sodium aluminate, and aluminium esters such asaluminium trialkoxides of formula Al(OR)₃ in which R denotes a C₁ -C₄alkyl radical such as methyl, ethyl or propyl.

The source of hydroxide ions is chosen from strong inorganic bases,especially hydroxides of the alkali metals of group IA of the PeriodicClassification of the Elements and hydroxides of the alkaline-earthmetals Ca, Sr and Ba, and strong organic bases, especially quaternaryammonium hydroxides, preference being given to inorganic bases andespecially to sodium hydroxide NaOH.

The reaction mixture intended to form the alumonisilicate gel may alsocontain M^(n+) cations of at least one metal M, of valency n, other thanthe metals whose hydroxides are strong bases, in an overall quantitysuch as to make the molar ratio M^(n+),:Al^(III) not exceed 0.4 andpreferably not exceed 0.3. The said M^(n+) cations are introduced intothe said reaction mixture in the form of salts such as sulphates,nitrates, chlorides or acetates or else in the form of oxides.

Examples of such cations which may be mentioned are especially Co⁺⁺,Cd⁺⁺, Mg⁺⁺ and Ag⁺.

Mixing of the ingredients constituting the reaction mixture intended toform the aluminosilicate gel may be performed in any order. The saidmixing is advantageously carried out by preparing first of all, at roomtemperature, a basic aqueous solution containing a strong base, thestructuring agent ST and the cations M^(n+) if they are employed, and inthen incorporating into this solution an aqueous solution of the sourceof trivalent aluminium and an aqueous solution or a suspension,colloidal or otherwise, of the source of tetravalent silicon.

The pH of the reaction mixture, whose value is higher than 10, ispreferably close to 13.

Before proceeding to crystallize the gel, crystallization seeds may beadded to the reaction mixture intended to form the said gel, in aquantity advantageously ranging from 0.1% to 10% by weight of thereaction mixture. These seeds may be produced either by grinding azeolite of the same kind as the crystalline phase to be produced or elseby synthesis from a suitable nucleating solution. For example, anappropriate nucleating solution has the following composition, expressedas oxides:

    15 Na.sub.2 O; 1 Al.sub.2 O.sub.3 ; 10 SiO.sub.2 ; 180 H.sub.2 O

In the absence of addition of seeds, it is advantageous to subject thealuminosilicate gel formed from the reaction mixture to a maturingoperation in a closed vessel, at a temperature below the crystallizationtemperature for a period which may range from approximately 6 hours toapproximately 6 days. The said maturing may be carried out in a staticregime or with stirring.

The crystallization of the aluminosilicate gel, with or without seed, iscarried out by heating the reaction mixture to a temperature notexceeding 150° C. and preferably ranging from 90° C. to 120° C. and at apressure corresponding at least to the autogenous pressure of thereaction mixture forming the gel. The heating period needed for thecrystallization depends on the composition of the gel and on thecrystallization temperature. It is generally between 2 hours and afortnight.

The crystals obtained, referred to as zeolite precursors and consistingof the zeolite trapping the structuring agent in its pores and cavities,are separated from the crystallization medium by filtration and are thenwashed with distilled or deionized water until weakly basic wash liquorsare obtained, that is to say whose pH is lower than 9. The washedcrystals are then dried in an oven at a temperature of between 50° C.and 100° C. and preferably in the region of 70° C.

The zeolite is obtained from the crystals of the precursor by subjectingthe said crystals to a calcination at a temperature above 300° C. andpreferably between 400° C. and 700° C. for a sufficient period of timeto remove the structuring agent present in the precursor.

As indicated earlier, the zeolites prepared by the process according tothe invention have Si:Al ratios higher than 1 and capable of exceeding 3and, depending on the nature of the structuring agent, may be eitherzeolites of the faujasite type exhibiting a structure of cubic symmetryor else hexagonal polytype zeolites of faujasite exhibiting a structureof hexagonal symmetry or else products made up of domains correspondingto a cubic faujasite and of domains corresponding to a hexagonalfaujasite.

The characterization of the products according to the invention, namelythe precursors resulting from the crystallization and the zeolitesproper resulting from the calcination of the precursors, can beperformed by employing the following techniques:

Electron microscopy

In the electron microscope, the products of cubic structure are seen informs which are compatible with cubic symmetry (for example regularoctahedra), whereas products of hexagonal structure are seen in formswhich are compatible with hexagonal structure (for example hexagonalplatelets).

X-ray diffraction pattern

This diffraction pattern is obtained by means of a diffractometer usingthe traditional powder method with copper Kα radiation. An internalstandard enables the values of the angles 2θ associated with thediffraction peaks to be determined accurately. The various latticespacing distances d_(hkl), characteristic of the sample, are calculatedfrom the Bragg relationship. The estimate of the error of measurementΔ(D_(hkl)) over d_(hkl) is calculated, as a function of the absoluteerror Δ(2θ) associated with the measurement of 2θ, using the Braggrelationship. In the presence of an internal standard, this error isreduced to a minimum and commonly taken as equal to ±0.05°. The relativeintensity I/Io associated with each d_(hkl) value is estimated from theheight of the corresponding diffraction peak. A scale of notations isemployed to characterize this relative intensity as follows: VS=verystrong, S=strong, mS=medium strong, m=medium, mw=medium weak, w=weak,vw=very weak.

Thermogravimetry

The thermograms obtained with the product samples make it possible toquantify the number of molecules of structuring agent and the number ofmolecules of water present in a unit cell of the structure.

Carbon 13 NMR

Carbon 13 NMR in crossed polarization with rotation at the magic angleperformed on the samples of the precursor enables the presence of thestructuring agent in the cavities of the product to be confirmed.

Determination of the Si:Al ratio

This can be carried out by resorting to any one of the followingtechniques:

chemical analysis

radiocrystallography (cf. D. W. Breck: "Zeolite Molecular Sieves", publ.John Wiley and Sons, New York, 1974, page 94)

silicon 29 NMR (cf. J. Klinowski: "Progress in NMR Spectroscopy", 1984,Vol. 16, pages 237 to 309).

The zeolites according to the invention of the faujasite type withstructure of cubic symmetry exhibit a cubic unit cell parameter a valueof between 2.4 and 2.5 nm.

These cubic zeolites can be given the following formula (I), reduced toa unit cell (assembly of 192 tetrahedra):

    (vM.sub.1.sup.q+) (wM.sup.n+) ((SiO.sub.2).sub.192-x (AlO.sub.2).sub.x).sup.x- (z H.sub.2 O)                   (I)

with, in this formula, M₁ ^(q+) denoting a q-valent cation of a metal ofgroup IA of the Periodic Classification of the Elements (q=1) or of analkaline-earth metal chosen from Ca, Sr and Ba (q=2) or a monovalentcation containing nitrogen (q=1), especially ammonium or quaternaryammonium, M^(n+) denoting a metal cation of valency n other than acation M₁ ^(q+), x, z, w and v being numbers such that 30<x≦96, Z≧0according to the hydration state of the zeolite (z=0 for a completelyanhydrous zeolite), 0<v≦x/q and 0≦w≦x/n with qv+wn≧x.

The zeolites according to the invention of the faujasite hexagonalpolytype type have a structure of hexagonal symmetry which has hexagonalunit cell parameters a, b and c such that 1.72<a=b<1.77 nm and2.80<c<2.89 nm.

These hexagonal polytypes can be given the following formula (II)reduced to a unit cell (assembly of 96 tetrahedra):

    (u M.sub.1.sup.q+) (r M.sup.n+) ((Sio.sub.2).sub.96-y (AlO.sub.2).sub.y).sup.y- (t H.sub.2 O)                   (II)

with, in this formula, M₁ ^(q+) denoting a q-valent cation of a metal ofgroup IA of the Periodic Classification of the Elements (q=1) or of analkaline-earth metal chosen from Ca, Sr and Ba (q=2) or a monovalentcation containing nitrogen (q=1), especially ammonium or quaternaryammonium, M^(n+) denoting a metal cation of valency n other than acation, M₁ ^(q+), y, t, u and r being numbers such that 15≦y≦48, t≧0according to the hydration state of the zeolite (t=0 for a completelyanhydrous zeolite), 0<u≦y/q and 0≦r≦y/n with qu+rn≧y.

In the interlayered products, the phases or domains exhibiting astructure corresponding to that of a faujasite with structure of cubicsymmetry can also be denoted by the formula (I), while the phases ordomains exhibiting a structure corresponding to that of a faujasitehexagonal polytype can also be denoted by the formula (II).

Tables I and II below show the characteristic x-ray diffraction patternof the cubic zeolites of the faujasite type (Table I) or of thefaujasite hexagonal polytypes (Table II), after the products have beencalcined for 4 hours at 600° C.

In the d_(hkl) column average values of the lattice spacing distanceshave been given. Each of these values must be associated with themeasurement error Δ(d_(hkl)) of between ±0.2 and ±0.008.

The variations which can be observed in relation to these average valuesare essentially linked with the nature of the compensating cations andwith the Si:Al ratio of the zeolite. The same remarks apply to therelative intensities I/Io.

                  TABLE I                                                         ______________________________________                                        2θ (degrees)                                                                       d.sub.hkl (10.sup.-1 nM)                                                                      (hkl)   I/Io                                       ______________________________________                                         6.245     14.14     ± 0.2  (1 1 1)                                                                             VS                                       10.205      8.66               (2 2 0)                                                                             S                                        11.965      7.39               (3 1 1)                                                                             mS                                       15.735      5.627    ± 0.05 (3 3 1)                                                                             S                                        18.775      4.721              (5 1 1)                                                                             w                                        20.465      4.335              (4 4 0)                                                                             mw                                       22.895      3.881              (6 2 0)                                                                             w                                        23.755      3.727              (5 3 3)                                                                             mS                                       25.105      3.544              (4 4 4)                                                                             vw                                       25.965      3.428              (5 5 1)                                                                             vw                                       27.175      3.279              (6 4 2)                                                                             mS                                       27.885      3.196    ± 0.008                                                                              (7 3 1)                                                                             vw                                       29.765      2.999              (7 3 3)                                                                             w                                        ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        2θ (°)                                                                   d.sub.hkl (10.sup.-1 nM)                                                                        (h k l) I/Io                                        ______________________________________                                         5.88   15.03      ± 0.2   (1 0 0)                                                                             VS                                         6.23   14.2                  (0 0 2)                                                                             VS                                         6.66   13.3                  (1 0 1)                                                                             S                                          8.40   10.52                 (1 0 2)                                                                             w                                         10.19   8.68       ± 0.08  (1 1 0)                                                                             S                                         11.06   7.99                  (1 0 3)                                                                             mS                                        11.78   7.51                  (2 0 0)                                                                             mS                                        11.95   7.40                  (1 1 2)                                                                             mS                                        13.49   6.56                  (2 0 2)                                                                             vw                                        15.06   5.88       ± 0.05  (2 0 3)                                                                             w                                         15.58   5.68                  (0 0 5)                                                                             S                                         15.89   5.57                  (2 1 1)                                                                             w                                         16.73   5.29                  (1 0 5)                                                                             w                                         17.18   5.16                  (2 0 4)                                                                             S                                         18.22   4.87                  (2 1 3)                                                                             w                                         18.79   4.72                  (1 1 5)                                                                             w                                         19.67   4.51                  (1 0 6)                                                                             w                                         20.45   4.34                  (2 2 0)                                                                             mS                                        22.22   4.00                  (3 1 2)                                                                             w                                         22.75   3.91                  (1 0 7)                                                                             w                                         23.30   3.82                  (3 1 3)                                                                             w                                         23.66   3.76                  (3 0 5)                                                                             S                                         24.75   3.59                  (3 1 4)                                                                             w                                         25.83   3.45                  (2 2 5)                                                                             w                                         26.52   3.36                  (2 1 5)                                                                             w                                         27.16   3.28                  (4 1 0)                                                                             w                                         28.77   3.103      ± 0.008 (3 2 4)                                                                             w                                         30.38   2.942                 (4 0 6)                                                                             vw                                        30.89   2.894                 (3 3 0)                                                                             w                                         31.20   2.866                 (5 0 3)                                                                             w                                         31.56   2.834                 (3 3 2)                                                                             vw                                        ______________________________________                                    

The precursors of zeolites, which are produced during thecrystallization stage of the process according to the invention andwhose calcination produces the zeolites whose formulae were definedabove, are crystalline aluminosilicates exhibiting an Si:Al ratio higherthan 1 and capable of exceeding 3, which have either the cubic structureof the faujasite corresponding to an x-ray diffraction patterncomparable with that given in Table III or else the hexagonal structureof the faujasite hexagonal polytypes corresponding to an x-raydiffraction pattern comparable to that given in Table IV, or elseinclude phases or domains exhibiting the structure of a cubic faujasitecorresponding to an X-ray diffraction pattern comparable to that givenin Table III and phases or domains exhibiting the structure of ahexagonal faujasite corresponding to an x-ray diffraction patterncomparable with that given in Table IV and which have cavities orchannels trapping structurant molecules ST which are molecules MC ormixtures of molecules MC and of costructurant CS.

The precursors exhibiting the structure of cubic symmetry of faujasitecan be denoted by a formula which, reduced to a unit cell of the cubicstructure, is written as follows:

    (v M.sub.1.sup.q+) (w M.sup.n+) ((SiO.sub.2).sub.192-x (AlO.sub.2).sub.x).sup.x- (p ST.sub.1) (z H.sub.2))

and in which M₁ ^(q+), M^(n+), x, v, w and z have the meanings givenearlier, p is a number such that 4≦p≦10 and ST₁ denotes a molecule of atleast one compound MC₁ chosen from the carbon-containing macroringscontaining from 10 to 17 atoms and carbon-containing macropolyringscontaining 10 to 18 atoms in each ring, the said macrorings andmacropolyrings additionally containing in the ring(s) heteroatoms chosenfrom O, S, N and Si, or of a mixture of at least one compound MC₁ and ofa costructurant CS consisting of at least one compound of formula

    R.sub.1 --O--C.sub.m H.sub.2m-1 X--O].sub.8 R.sub.2

in which R₁, R₂, X, m and g have the meanings given above.

                  TABLE III                                                       ______________________________________                                        2θ (°)                                                                   d.sub.hkl (10.sup.-1 nM)                                                                       (h k l) I/Io                                         ______________________________________                                         6.26   14.10      ± 0.2   (1 1 0)                                                                             VS                                        10.23   8.65                  (2 2 0)                                                                             w                                         12.01   7.35                  (3 1 1)                                                                             mS                                        15.77   5.615      ± 0.05  (3 3 1)                                                                             S                                         18.81   4.713                 (5 1 1)                                                                             m                                         20.49   4.331                 (4 4 0)                                                                             mS                                        22.93   3.875                 (6 2 0)                                                                             w                                         23.77   3.740                 (5 3 3)                                                                             mS                                        25.15   3.537                 (4 4 4)                                                                             vw                                        25.93   3.433                 (5 5 1)                                                                             vw                                        27.19   3.276                 (6 4 2)                                                                             mS                                        27.93   3.191      ± 0.008 (7 3 1)                                                                             vw                                        29.81   2.994                 (7 3 3)                                                                             w                                         ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        2θ (°)                                                                    d.sub.hkl (10.sup.-1 nM)                                                                      (h k l) I/Io                                         ______________________________________                                         5.88    15.02     ± 0.2  (1 0 0)                                                                             VS                                          6.24    14.15               (0 0 2)                                                                             S                                           6.65    13.28               (1 0 1)                                                                             S                                          10.12    8.73      ± 0.08 (1    )                                                                             w                                          11.01    8.03                (1 0 3)                                                                             mw                                         11.93    7.41                (1 1 2)                                                                             mS                                         13.58    6.515               (2 0 2)                                                                             vw                                         15.57    5.686     ± 0.05 (0 0 5)                                                                             mS                                         15.86    5.580               (2 1 1)                                                                             mw                                         16.70    5.305               (1 0 5)                                                                             mw                                         17.15    5.165               (2 0 4)                                                                             S                                          18.16    4.88                (2 1 3)                                                                             mw                                         18.71    4.74                (1 1 5)                                                                             mw                                         19.65    4.509               (1 0 6)                                                                             mS                                         20.42    4.345               (2 2 0)                                                                             S                                          22.14    4.011               (3 1 2)                                                                             mS                                         22.71    3.912               (1 0 7)                                                                             mw                                         23.32    3.811               (3 1 3)                                                                             mw                                         23.60    3.766               (3 0 5)                                                                             mw                                         24.68    3.604               (3 1 4)                                                                             mw                                         25.81    3.449               (2 2 5)                                                                             w                                          26.49    3.362               (2 1 5)                                                                             w                                          ______________________________________                                    

The precursors exhibiting the hexagonal symmetry structure of thehexagonal polytypes of faujasite can be represented by a formula which,reduced to a hexagonal unit cell of the crystalline structure, iswritten as follows:

    (u M.sub.1.sup.q+) (r M.sup.n+) ((SiO.sub.2).sub.96-y (AlO.sub.2).sub.y).sup.y- (j ST.sub.2) (t H.sub.2 O)

in which, M₁ ^(q+), M^(n+), y, u, r and t have the meanings givenearlier, j is a number such that 2≦j≦5 and ST₂ denotes a molecule of atleast one compound MC₂ chosen from carbon-containing macrorings whosering contains heteroatoms chosen from O, N, Si and S and whose ringcontains at least 18 atoms.

The molecules forming the structuring agents ST, ST₁ and ST₂ may bechosen especially from crown ethers whose ring contains at least fouroxygen atoms, the compounds having a structure comparable to those ofcrown ethers but whose ring oxygen atoms are partially or whollyreplaced by substituents chosen from sulphur atoms and >NH, >NR and>Si<_(R) ^(R) groups in which R is a monovalent C₁ -C₄ hydrocarbonradical or else from carbon-containing macropolyrings of the type ofpolyoxadiazabicycloalkanes in which each ring contains 10 to 18 atomsand has at least two oxygen atoms in addition to the two nitrogen atomsand also, in the case of the structuring agents ST and ST₁, from theassociations of such molecules with molecules forming the costructurantCS. Molecules which are particularly suitable for forming thestructuring agents ST, ST₁ and ST₂ are those referred to aboveexplicitly for this purpose.

The zeolites obtained by the process according to the invention can beemployed in applications of the same type as the zeolites of similarstructure and of comparable or lower Si:Al ratio which are prepared byclosely related or different methods.

Thus, the zeolites obtained according to the invention are suitable asan adsorbent for performing the selective adsorption of molecules whosedimensions are below 0.8 nM or else, after having been subjected toexchange reactions with various cations, as catalysts or components ofcatalysts which can be employed in catalytic conversion reactions oforganic compounds and especially of hydrocarbon compounds. For example,the protonated form of the zeolite is obtained by an exchange treatmentwith ammonium cations followed by a calcination. This form, as well asthose resulting from an exchange treatment with rare-earth cations suchas lanthanum are suitable as acidic catalysts for hydrocrackingpetroleum chargers. The zeolites can also be subjected to exchangetreatments with cations of metals of groups II to VIII of the PeriodicClassification to form products which are suitable as catalysts forhydrocarbon conversion. For their application as catalysts, zeolitesmodified by exchange with cations endowing them with catalyticproperties may be employed by themselves or in the form of compositeproducts resulting from the mixing of these modified zeolites with othercatalytically active products and/or with an amorphous matrix such as asilica gel or else a mixed gel of silica and of another oxide such asmagnesia, alumina, titanium oxide or zirconium oxide, the said matrixbeing used, inter alia, to impart a better heat stability to thecatalyst.

Composite catalysts associating one or more catalytically activezeolites with a matrix based on silica gel or a mixed gel of silica andof another oxide are particularly suitable for operations in a movingbed or in a fluidized bed, because they can be easily shaped, forexample by spray-drying an aqueous suspension of the ingredients ofwhich they are composed, into granules which have the dimensionsrequired for these operations.

The following examples are given without any limitation being implied toillustrate the invention.

In these examples the quantities and percentages are given by weightunless shown otherwise.

EXAMPLE 1 Synthesis of a hexagonal polytype of faujasite

An aluminosilicate gel was prepared first of all by operating as followsin a vessel of appropriate capacity, the contents of the said vesselbeing kept stirred throughout the operation. 9 parts of water followedby 0.75 parts of sodium hydroxide NaOH were introduced into the vesseland, after the sodium hydroxide dissolved, 1.45 parts of 18-crown-6ether were introduced. After the crown ether had dissolved completely, 1part of a sodium aluminate containing 56% of Al₂ O₃ and 37% of Na₂ O wasthen added to the contents of the vessel and the reaction mixture washeated slightly to dissolve the aluminate completely. After return toroom temperature, 8.2 parts of a colloidal suspension of silicacontaining 40% of SiO₂ and 60% of water were then introduced into thevessel.

An aluminosilicate gel was thus obtained, whose molar composition,reduced to one mole of Al₂ O₃, was the following:

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.8 Na.sub.2 O; 1 crown ether; 140 H.sub.2 O.

The gel obtained was subjected to a maturing operation at roomtemperature for 48 hours in a closed vessel.

The matured gel was then placed in an autoclave and kept in the latterat 110° C. for 96 hours to form a crystalline product. The crystalsformed were separated off from the reaction medium by filtration andwere then washed with distilled water to a low basicity (pH below 9) ofwash liquors and were finally dried in an oven at approximately 60° C.

The dried crystals were then calcined at 600° C. for 4 hours in order toremove the molecules of the crown ether employed as structuring agentand to obtain the zeolite.

Before calcination the crystalline product has an x-ray diffractionpattern comparable to that given in Table IV.

The formula found for the said product, reduced to a unit cell of thestructure, which is of hexagonal symmetry, is written:

    21 Na.sup.+ ((SiO.sub.2).sub.75.6 (AlO.sub.2).sub.20.4).sup.20.4- 4(18-crown-6)67 H.sub.2 O.

The zeolite formed by calcining the above product has an x-raydiffraction pattern comparable to that in Table II characteristic of thecalcined hexagonal polytypes of faujasite.

The formula found for this zeolite, reduced to a unit cell of thehexagonal skeleton, is written in the anhydrous state:

    21 Na.sup.+ ((SiO.sub.2).sub.75.6 (AlO.sub.2).sub.20.4).sup.20.4-

A very slight excess of positive charge is found in relation toneutrality.

Approximately 80% of the silica used in the operation is found again inthe skeleton of the zeolite.

EXAMPLE 2 Synthesis of a hexagonal polytype of faujasite

The procedure was as shown in Example 1, but with the following changesin the operating conditions:

    ______________________________________                                        gel preparation                                                                              0.48 parts of sodium hydroxide                                                and 0.7 parts of 18-crown-6                                                   ether                                                          maturing       24 hours at 20° C.                                      crystallization                                                                              110° C. for 144 hours                                   calcination    400° C. for 6 hours                                     ______________________________________                                    

Before maturing, the aluminosilicate gel had the following molarcomposition, reduced to 1 mole of Al₂ O₃ : 10 SiO₂ ; 1 Al₂ O₃ ; 2.2 Na₂O; 0.5 crown ether; 140 H₂ O

Before calcination the crystalline product has an x-ray diffractionpattern comparable to that given in Table IV.

The formula found for the said product, reduced to a unit cell of thestructure, which is of hexagonal symmetry, is written:

    19 Na.sup.+ ((SiO.sub.2).sub.77.2 (AlO.sub.2).sub.18.8).sup.18.8- 3.9 (18-crown-6)66 H.sub.2 O

The zeolite formed by calcining the above product exhibits an x-raydiffraction pattern comparable to that of Table II, characteristic ofthe calcined hexagonal polytypes of faujasite.

The formula found for this zeolite, reduced to a unit cell of thehexagonal structure, is written in the anhydrous state:

    19 Na.sup.+ ((SiO.sub.2).sub.77.2 (AlO.sub.2).sub.18.8).sup.18.8-

Approximately 80% of the silica used in the operation is found again inthe skeleton of the zeolite.

EXAMPLE 3 Synthesis of a hexagonal polytype of faujasite

The procedure was as shown in Example 1, but with the following changesin the operating conditions:

    ______________________________________                                        gel preparation                                                                             0.57 parts of sodium hydroxide,                                               1 part of 18-crown-6 ether and                                                0.25 parts of a cobalt acetate                                                containing 24% of cobalt and 29%                                              of water, the acetate being                                                   added after dissolving the crown                                              ether and before adding the                                                   aluminate                                                       maturing      24 hours at room temperature                                    crystallization                                                                             110° C. for 144 hours                                    calcination   600° C. for 6 hours.                                     ______________________________________                                    

Before maturing, the aluminosilicate gel had the following molarcomposition, reduced to 1 mole of Al₂ O₃ : 10 SiO₂ ; 1 Al₂ O₃ ; 2.4 Na₂O; 0.7 crown ether; 0.1 CoO; 140 H₂ O.

Before calcining, the crystalline product exhibits an X-ray diffractionpattern comparable with that given in Table IV.

The formula found for the said product, reduced to a unit cell of thestructure, which is of hexagonal symmetry, is written: ##EQU1## withε=0.1 in this formula.

The zeolite formed by calcining the above precursor product exhibits anx-ray diffraction pattern comparable with that given in Table II,characteristic of the calcined hexagonal polytypes of faujasite.

The formula determined for this zeolite reduced to a unit cell of thehexagonal structure, is written in the anhydrous state: ##EQU2## withβ<0.1 in this formula.

Approximately 90% of the silica used in the operation is found again inthe skeleton of the zeolite.

EXAMPLE 4 Synthesis of a hexagonal polytype of faujasite

The procedure was as shown in Example 3, but with cobalt acetatereplaced with 0.2 parts of silver nitrate and performing the calcinationof the zeolite precursor at 400° C. for 6 hours.

Before maturing, the aluminosilicate gel had the following molarcomposition, reduced to 1 mole of Al₂ O₃ : 10 SiO₂ ; 1 Al₂ O₃ ; 2.4 Na₂O; 0.5 crown ether; 0.1 Ag₂ O; 140 H₂ O

Before calcination the crystalline product exhibits an x-ray diffractionpattern comparable with that given in Table IV.

The formula determined for the said product, reduced to a unit cell ofthe structure, which is of hexagonal symmetry, is written ##EQU3## withε<0.1 in this formula.

The zeolite formed by calcining the above precursor product exhibits anx-ray diffraction pattern comparable with that given in Table II,characteristic of the calcined hexagonal polytypes in faujasite.

The formula determined for this zeolite, reduced to a unit cell of thehexagonal structure, is written in the anhydrous state: ##EQU4## withε<0.1 in this formula.

Approximately 90% of the silica used in the operation is found again inthe skeleton of the zeolite.

EXAMPLE 5 Synthesis of a cubic faujasite

The procedure was as shown in Example 1, but with the following changesin the operating conditions:

    ______________________________________                                        gel preparation                                                                              0.66 parts of sodium hydroxide                                                and 0.84 parts of 15-crown-5                                                  ether                                                          maturing        24 hours at room temperature                                  crystallization                                                                              100 hours at 110° C.                                    calcination    400° C. for 4 hours.                                    ______________________________________                                    

Before maturing, the aluminosilicate gel had the following molarcomposition, reduced to 1 mole of Al₂ O₃ : 10 SiO₂ ; 1 Al₂ O₃ ; 2.6 Ha₂O; 0.7 crown ether; 140 H₂ O.

Before calcination the crystalline product exhibits an X-ray diffractionpattern comparable with that given in Table III.

The formula determined for the said product, reduced to a unit cell ofthe structure, which is of cubic symmetry, is written:

    40 Na.sup.+ ((SiO.sub.2).sub.152.8 (AlO.sub.2).sub.39.2).sup.39.2- 7.6(15-crown-5) 135 H.sub.2 O.

The zeolite formed by calcining the above product exhibits an X-raydiffraction pattern comparable to that of Table I, characteristic of thecalcined cubic zeolites of the faujasite type.

The formula determined for this cubic zeolite, reduced to a unit cell ofthe cubic structure, is written in the anhydrous state:

    40 Na.sup.+ ((SiO.sub.2).sub.152.8 (AlO.sub.2).sub.39.2).sup.39.2-.

Approximately 80% of the silica used in the operation is found again inthe skeleton of the zeolite.

EXAMPLE 6 Synthesis of a cubic faujasite

The procedure was as shown in Example 1, but with the following changesin the operating conditions

    ______________________________________                                        gel preparation                                                                              0.57 parts of sodium hydroxide                                                and 1.2 parts of 15-crown-5                                                   ether                                                          crystallization                                                                              192 hours at 115° C.                                    calcination    500° C. for 4 hours.                                    ______________________________________                                    

Before maturing, the aluminosilicate gel had the following molarcomposition, reduced to 1 mole of Al₂ O₃ : 10 SiO₂ ; 1 Al₂ O₃ ; 2.4 Na₂O; 1 crown ether; 140 H₂ O.

Before calcination the crystalline product exhibits an X-ray diffractionpattern comparable with that given in Table III corresponding to astructure of cubic symmetry.

The formula determined for the said product, reduced to a unit cell ofthe cubic structure, is written:

    36 Na.sup.+ ((SiO.sub.2).sub.156.4 (AlO.sub.2).sub.35.6).sup.35.6- 7.7 (15-crown-5) 133 H.sub.2 O

The zeolite formed by calcining the above product exhibits an X-raydiffraction pattern comparable with that of Table I, characteristic ofthe calcined cubic zeolites of the faujasite type.

The formula determined for this cubic zeolite, reduced to a unit cell ofthe cubic structure, is written in the anhydrous state:

    36 Na.sup.+ ((SiO.sub.2).sub.156.4 (AlO.sub.2).sub.35.6).sup.35.6-

Approximately 85% of the silica used in the operation is found again inthe skeleton of the zeolite.

EXAMPLE 7 Synthesis of a cubic faujasite

An aluminosilicate gel was prepared first of all by operating as followsin a glass vessel of suitable capacity, the contents of the said vesselbeing kept stirred throughout the operation. Into the vessel wereintroduced 1.8 parts of distilled water, 0.12 parts of a sodiumaluminate containing 56% of Al₂ O₃ and 37% of Na₂ O, 0.3 parts of amacropolyring marketed under the name "Kryptofix 2.2.2" and 0.12 partsof sodium hydroxide. When the contents of the vessel were clear inappearance, 1.64 parts of a colloidal suspension of silica containing40% of SiO₂ and 60% of water were then added slowly thereto.

An aluminosilicate gel was thus obtained, whose molar composition,reduced to 1 mole of Al₂ O₃, was the following: 10 SiO₂ ; 1 Al₂ O₃ ; 2.4Na₂ O; 0.7 macropolyring; 140 H₂ O

The gel obtained was subjected to a maturing operation of 24 hours atambient temperature in a closed vessel.

The matured gel was then placed in an autoclave and kept in the latterat 115° C. for 10 days to form a crystalline product. The resultingproduct was separated off from the reaction medium by filtration and wasthen washed with distilled water until the wash liquors had a pH below 9and was finally dried in an oven at approximately 60° C.

The product obtained consisted of a mixture of a crystalline phase andan amorphous phase.

The crystalline phase exhibits an x-ray diffraction spectrumcorresponding to that of a faujasite of cubic symmetry and rich insilicon, the Si:Al ratio of the said crystalline phase beingapproximately 4. The crystals making up this crystalline phase areisometric entities of 3 to 7 μm exhibiting no extraction.

EXAMPLE 8 Synthesis of a cubic faujasite

An aluminosilicate gel was prepared by proceeding as described inExample 1, but using only 0.66 parts of sodium hydroxide and replacingthe 18-crown-6 ether with 1.61 parts of dimethylsila-17-crown-6 ether.

The gel obtained was subjected to a maturing operation for 24 hours at25° C.

The matured gel was then placed in an autoclave and kept in the latterat 115° C. for 6 days for the purpose of crystallization. The resultingproduct was then separated off from the reaction medium by filtrationand was then washed with distilled water until the wash liquors had a pHbelow 9 and was finally dried in an oven at approximately 60° C.

The product obtained consisted of a mixture of a crystalline phase andan amorphous phase.

After calcination at 600° C. for 4 hours, the crystalline phase exhibitsan x-ray diffraction spectrum comparable with that given in Table I,characteristic of a faujasite of cubic symmetry, the Si:Al ratio of thesaid crystalline phase being approximately 4.

Example 9 Synthesis of a hexagonal polytype of faujasite

The procedure was as shown in Example 1, but with the following changesin the operating conditions:

    ______________________________________                                        gel preparation                                                                              0.84 parts of sodium hydroxide,                                               1 part of 18-crown-6 ether and                                                9.9 parts of the silica                                                       suspension                                                     maturing       24 hours at room temperature                                                  with stirring                                                  crystallization                                                                              15 days at 115° C.                                      ______________________________________                                    

Before maturing, the aluminosilicate gel had the following molarcomposition, reduced to 1 mole of Al₂ O₃ : 12 SiO₂ ; 1 Al₂ O₃ ; 3.8 Na₂O; 0.7 crown ether; 140 H₂ O

The crystalline product was in the form of more or less sphericalcrystals 10 to 13 μm in diameter.

Before calcination the crystalline product exhibits an x-ray diffractionpattern comparable with that given in Table IV.

The formula found for the said product, reduced to a unit cell of thestructure, which is of hexagonal symmetry, is written:

    19 N.sup.+ ((SiO.sub.2).sub.77.6 (AlO.sub.2).sub.18.4).sup.18.4- 4.1 (18-crown-6) 68 H.sub.2 O

The zeolite formed by calcining the above product exhibits an x-raydiffraction pattern comparable with that of Table II, characteristic ofthe calcined hexagonal polytypes of faujasite.

The formula found for this zeolite, reduced to a unit cell of thehexagonal structure, is written in the anhydrous state:

    19 Na.sup.+ ((SiO.sub.2).sub.77.6 (AlO.sub.2).sub.18.4).sup.18.4-

Approximately 85% of the silica used in the operation is found again inthe skeleton of the zeolite, whose Si:Al ratio is approximately 4.3.

EXAMPLE 10 Synthesis of a hexagonal polytype of faujasite with the useof crystallization seeds

An aluminosilicate gel was prepared by proceeding as shown in Example 1,but using 0.48 parts of sodium hydroxide and 1 part of 18-crown-6 ether.

The gel obtained had the following molar composition, reduced to 1 moleof Al₂ O₃ :

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.2 Na.sub.2 O; 0.7 crown ether; 140 H.sub.2 O

The abovementioned gel was subjected to a maturing operation for 5 hoursat 25° C.

The seeds were prepared separately by grinding finely crystals of thecalcined hexagonal polytype obtained in Example 1. 0.2 parts of theseeds obtained, to which 0.3 parts of sodium hydroxide had been addedwere then added to the matured gel.

The mixture thus produced was then kept in an autoclave heated to 115°C. for a period of 55 hours for the purpose of crystallization.

The crystals obtained were separated off from the reaction medium andwere then washed, dried and calcined as shown in Example 1.

Before calcination the crystalline product exhibits an x-ray diffractionpattern comparable with that given in Table IV.

The formula found for the said product, reduced to a unit cell of thestructure, which is of hexagonal symmetry, is written:

    19 Na.sup.+ ((SiO.sub.2).sub.77.3 (AlO.sub.2).sub.18.7).sup.18.7- 3.9 (18-crown-6) 67 H.sub.2 O.

The zeolite formed by calcining the above product exhibits an x-raydiffraction pattern comparable with that given in Table II,characteristic of the calcined hexagonal polytypes of faujasite.

Approximately 90% of the silica used in the operation is found again inthe skeleton of the zeolite.

EXAMPLE 11 Use of a structuring agent consisting of a mixture of15-crown-5 and 18-crown-6 ethers

An aluminosilicate gel was prepared first of all by proceeding asfollows in a vessel of suitable capacity, the contents of the saidvessel being kept stirred throughout the operation.

10 parts of water and then 0.3 parts of 18-crown-6 ether were introducedinto the vessel and, after the said crown ether had dissolvedcompletely, 0.5 parts of 15-crown-5 ether were added. After dissolvingof the second crown ether, 1 part of a sodium aluminate containing 56%of Al₂ O₃ and 37% of Na₂ O was then added to the contents of the vesseland the reaction mixture was heated slightly to dissolve the aluminatecompletely. After return to room temperature, 8.2 parts of a colloidalsuspension of silica containing 40% of SiO₂ and 60% of water were thenintroduced into the vessel.

An aluminosilicate gel was thus obtained, whose molar composition,reduced to one mole of Al₂ O₃, was the following:

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.4 Na.sub.2 O; 0.2 18-crown-6; 0.4 15-crown-5; 140 H.sub.2 O.

The gel obtained was subjected to a maturing operation at roomtemperature for 24 hours in a closed vessel. The matured gel was thenplaced in an autoclave and kept in the latter at 115° C. for 192 hoursto form a crystalline product. The crystals formed were separated offfrom the reaction medium by filtration and were then washed withdistilled water to a low basicity (pH below 9) of the washed liquors andwere finally dried in an oven at approximately 60° C.

The dried crystals were then calcined at 600° C. for 4 hours in order toremove the molecules of the crown ethers employed as structuring agentand to obtain the zeolite.

Before calcination the crystalline product is a zeolitic percursor ofthe faujasite type, which consists of a product made up of domains whichhave a structure of cubic symmetry and of domains which have a structureof hexagonal symmetry. The coefficient α, measured by x-ray diffraction,is equal to 0.2.

The formula found for the said product, reduced to a cubic unit cell of192 tetrahedra, is written 36.2 Na⁺ ((SiO₂)₁₅₆.5 (AlO₂)₃₅.5)⁻³⁵.5 1.3(18-crown-6) 6.2 (15-crown-5) 139 H₂ O

The zeolite formed by calcining the above precursor product is also aproduct made up of domains corresponding to a cubic faujasite and ofdomains corresponding to a hexagonal faujasite. The measured coefficientα is equal to 0.2. The formula determined for this zeolite, reduced to acubic unit cell of 192 tetrahedra, is written in the anhydrous state

    36.2 Na.sup.+ ((SiO.sub.2).sub.156.5 (AlO.sub.2).sub.35.5).sup.-35.5

Approximately 80% of the silica used is found again in the skeleton ofthe zeolite.

EXAMPLE 12 Use of a structuring agent consisting of a mixture of15-crown-5 and 18-crown-6 ethers

By proceeding in conditions similar to those of Example 11, analuminosilicate gel was prepared which, before maturing, had thefollowing molar composition, reduced to 1 mole of Al₂ O₃ :

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.2 Na.sub.2 O; 0.3 18-crown-6; 0.3 15-crown-5; 140 H.sub.2 O

The gel was then treated as described in Example 11 to produce thezeolite.

Before calcination the crystalline product is a zeolitic precursor offaujasite type, which consists of a product make up of domains whichhave a structure of cubic symmetry and of domains which have a structureof hexagonal symmetry. The measured coefficient α has a value equal to0.6.

The formula determined for this zeolitic precursor, reduced to a cubicunit cell of 192 tetrahedra, is the following:

    38.6 Na.sup.+ ((SiO.sub.2).sub.154.1 (AlO.sub.2).sub.37.9).sup.37.9- 4.5 (18-crown-6) 3.6 (15-crown-5) 139 H.sub.2 O

The zeolite formed by calcining the above precursor product is also aproduct made up of domains corresponding to a cubic faujasite and ofdomains corresponding to a hexagonal faujasite. The measured coefficientα has a value equal to 0.6.

The formula determined for this zeolite, reduced to a cubic unit cell of192 tetrahedra, is written in the anhydrous state:

    38.6 Na.sup.+ [(SiO.sub.2).sub.154.1 (AlO.sub.2).sub.37.9 ].sup.37.9-

EXAMPLE 19 Use of a structuring agent consisting of a mixture of18-crown-6 and 15-crown-5 ethers

By proceeding in conditions similar to those of Example 11, analuminosilicate gel was prepared which, before maturing, had thefollowing molar composition, reduced to 1 mole of Al₂ O₃ :

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.4 Na.sub.2 O; 0.4 18-crown-6; 0.2 15-crown-5; 140 H.sub.2 O

The gel was then treated as shown in Example 11 to produce the zeolite.

Before calcination the crystalline product is a zeolitic precursor offaujasite type, which consists of a product made up of domains whichhave a structure of cubic symmetry and of domains which have a structureof hexagonal symmetry. The measured coefficient α has a value equal to0.8.

The formula determined for this zeolitic precursor, reduced to a cubicunit cell of 192 tetrahedra, is the following:

    35.6 Na.sup.+ [(SiO.sub.2).sub.157.3 (AlO.sub.2).sub.34.7 ].sup.34.7- 6.7(18-crown-6) 1.4(15-crown-5) 129 H.sub.2 O

The zeolite formed by calcining the above precursor product is also aproduct made up of domains corresponding to a cubic faujasite and ofdomains corresponding to a hexagonal faujasite. The measured coefficientα is equal to 0.8.

The formula determined for this zeolite, reduced to a cubic unit cell of192 tetrahedra, is written in the anhydrous state

    36.6 Na.sup.+ [(SiO.sub.2).sub.157.3 (AlO.sub.2).sub.34.7 ].sup.34.7-

EXAMPLE 14 Use of a structuring agent consisting of a mixture of18-crown-6 and 12-crown-4 ethers

By proceeding in conditions similar to those of Example 11, analuminosilicate gel was prepared which, before maturing, had thefollowing molar composition, reduced to 1 mole of Al₂ O₃ :

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.3 Na.sub.2 O; 0.2 18-crown-6; 0.4 12-crown-4; 140 H.sub.2 O

The gel was then treated as shown in Example 11 to produce the zeolite,but by resorting to a maturing operation of 24 hours at 20° C. and to acrystallization of 12 days at 100° C.

Before calcination the crystalline product is a zeolitic precursor ofthe faujasite type, which consists of a product made up of domains whichhave a structure of cubic symmetry and of domains which have a structureof hexagonal symmetry. The measured coefficient α has a value of 0.55.

The formula determined for this zeolitic precursor, reduced to a cubicunit cell of 192 tetrahedra, is the following:

    37.2 Na.sup.+ [(SiO.sub.2).sub.156.5 (AlO.sub.2).sub.35.5 ].sup.35.5- 5.9(18-crown-6) 2.4 (12-crown-4) 140 (H.sub.2 O)

The zeolite formed by calcining the above precursor product is also aproduct exhibiting domains corresponding to a cubic faujasite anddomains corresponding to a hexagonal faujasite. The measured coefficientα has a value equal to 0.55.

The formula determined for this zeolite, reduced to a cubic unit cell of192 tetrahedra, is written in the anhydrous state

    37.2 Na.sup.+ [(SiO.sub.2).sub.156.5 (AlO.sub.2).sub.35.5 ].sup.35.5-

EXAMPLE 15 Use of a structuring agent consisting of a mixture of15-crown-5 ether and of "PEO₂₀₀ "

By proceeding as shown in Example 11, but using a structuring agent madeup of equimolar quantities of 15-crown-5 ether and of an acycliccostructurant referred to by the abbreviation of "PEO₂₀₀ " andconsisting of the monomethyl ether of a polyoxyethylene glycol ofnumber-average molecular mass Mn equal to 200, an alumino-silicate gelwas prepared which, before maturing, had the following composition,reduced to one mole of Al₂ O₃ : 10 SiO₂ ; 1 Al₂ O₃ ; 2.3 Na₂ O; 0.215-crown-5; 0.2 PEO₂₀₀ ; 140 H₂ O

The gel was then treated as shown in Example 11 to produce the zeolite,but with the maturing operation being carried out at 25° C. for 24 hoursand the crystallization at 100° C. for 12 days.

Before calcination, the crystalline product is a zeolitic precursor offaujasite type, exhibiting a structure of cubic symmetry.

The formula determined for this zeolitic precursor, reduced to a cubicunit cell of 192 tetrahedra, is the following:

    38.1 Na.sup.+ [(SiO.sub.2).sub.155 (AlO.sub.2).sub.37 ].sup.37- 5.6(15-crown-5)2(PEO.sub.200)153 H.sub.2 O

The zeolite formed by calcining the above precursor product is a zeoliteof faujasite type exhibiting a structure of cubic symmetry.

The formula determined for this zeolite, reduced to a cubic unit cell of192 tetrahedra, is written in the anhydrous state

    38.1 Na.sup.+ [(SiO.sub.2).sub.155 (AlO.sub.2).sub.37 ].sup.37-

Approximately 85% of the silica used is found again in the skeleton ofthe zeolite.

EXAMPLE 16 Use of a structuring agent consisting of a mixture of15-crown-5 ether and ethylene glycol

By proceeding as shown in Example 11, but using a structuring agent madeup of a mixture of 15-crown-5 ether and of an acyclic costructurantreferred to by the abbreviation of "EG" and consisting of ethyleneglycol, an aluminosilicate gel was prepared which, before maturing, hadthe following composition, reduced to 1 mole of Al₂ O₃ :

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.2 Na.sub.2 O; 0.2 15-crown-5; 2 EG; 140 H.sub.2 O

The gel was then treated as shown in Example 11 to produce the zeolite,the maturing being performed, however, at 20° C. for 24 hours and thecrystallization at 100° C. for 12 days.

Before calcination the crystalline product is a zeolitic precursor ofthe faujasite type, exhibiting a structure of cubic symmetry.

The formula determined for this zeolitic precursor, reduced to a cubicunit cell of 192 tetrahedra, is the following:

    38.5 Na.sup.+ [(SiO.sub.2).sub.155.1 (AlO.sub.2).sub.36.8 ].sup.36.8- 5.4(15-crown-5) 1.7(EG) 152 (H.sub.2 O)

The zeolite formed by calcining the above precursor product is a zeoliteof faujasite type, exhibiting a structure of cubic symmetry.

The formula determined for this zeolite, reduced to a cubic unit cell of192 tetrahedra, is written in the anhydrous state

    38.5 Na.sup.+ [(SiO.sub.2).sub.155.1 (AlO.sub.2).sub.36.8 ].sup.36.8-

EXAMPLE 17 Use of a structuring agent consisting of a mixture of18-crown-6 ether and ethylene glycol

By proceeding as shown in Example 11, but using a structuring agent madeup of a mixture of 18-crown-6 ether and of an acyclic costructurantreferred to by the abbreviation of "EG" and consisting of ethyleneglycol, an aluminosilicate gel was prepared which, before maturing, hadthe following composition, reduced to 1 mole of Al₂ O₃ :

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.2 Na.sub.2 O; 0.2 18-crown-6; 2 EG; 140 H.sub.2 O

The gel was then treated as shown in Example 11 to produce the zeolite,the maturing being performed, however, at 25° C. for 24 hours and thecrystallization at 100° C. for 12 days.

Before calcination, the crystalline product is a zeolitic precursor ofthe faujasite type, made up of domains which have a structure of cubicsymmetry and of domains which have a structure of hexagonal symmetry.

The measured coefficient α has a value equal to 0.85. The Si:Al ratio ofthe skeleton of the said precursor, determined by NMR of silicon 29 withrotation at the magic angle, is close to 4.

The zeolite obtained by calcining the above precursor product is azeolite of the faujasite type, exhibiting domains corresponding to cubicfaujasite and domains corresponding to a hexagonal faujasite. Themeasured coefficient α has a value equal to 0.85. The Si:Al ratio of theskeleton of the zeolite, determined by NMR of silicone 29 with rotationat the magic angle, is close to 4.

EXAMPLE 18 Use of a structuring agent consisting of a mixture of18-crown-6 ether and of "PEO₃₅₀ "

By proceeding as shown in Example 11, but using a structuring agent madeup of a mixture of 18-crown-6 ether and of a costructurant referred toby the abbreviation of "PEO₃₅₀ " and consisting of the monomethyl etherof a polyoxyethylene glycol of number-average molecular mass Mn equal to350, an aluminosilicate gel was prepared which, before maturing, had thefollowing composition, reduced to 1 mole of Al₂ O₃ :

    10 SiO.sub.2 ; 1 Al.sub.2 O.sub.3 ; 2.3 Na.sub.2 O; 0.2 18-crown-6; 0.2 PEO.sub.350 ; 140 H.sub.2 O

The gel was then treated as shown in Example 11 to produce the zeolite,the maturing being performed, however, at 20° C. for 24 hours and thecrystallization at 100° C. for 12 days.

Before calcination, the crystalline product is a zeolitic precursor ofthe faujasite type, made up of domains which have a structure of cubicsymmetry and of domains which have a structure of hexagonal symmetry.The measured coefficient α is close to 0.8.

The zeolite formed by calcining the above precursor product is a zeoliteof the faujasite type exhibiting domains corresponding to a cubicfaujasite and domains corresponding to a hexagonal faujasite. Themeasured coefficient α is close to 0.8. The Si:Al ratio of the skeletonof the zeolite, determined by NMR of silicon 29 with rotation at themagic angle, is close to 4.

We claim:
 1. A process for the preparation of zeolites belonging to thefaujasite structural class and exhibiting a Si:Al ratio higher than 1,said process comprising first forming a reaction mixture which has a pHhigher than 10 and contains water, a source of tetravalent silicon, asource of trivalent aluminum, a source of hydroxide ions in the form ofa strong inorganic or organic base and a structural agent ST so as toproduce an alumino silicate gel having the composition to permit itscrystallization into a compound of the faujasite structural class, andthe gel obtained is then kept at a temperature not exceeding 150° C. andat a pressure of at least equal to the autogenous pressure of said gelfor a sufficient period to effect the crystallization of said gel into aprecursor of the zeolite consisting of the zeolite with the structuralagent ST trapped in its cavities and said precursor is subjected to acalcination to destroy said structuring agent ST and to produce thezeolite, and wherein the structuring agent ST consists of at least onecompound MC selected from the group consisting of carbon-containingmacrorings and macropolyrings which contain in the rings heteroatomsselected from the group consisting of oxygen, nitrogen, silicon, andsulfur, and which contain 10 to 24 atoms per ring.
 2. The processaccording to claim 1, wherein the quantity of structuring agent ST inthe reaction mixture intended to form the gel is such as to make themolar ratio ST:Al^(III) ranged from 0.1 to
 4. 3. The process accordingto claim 1, wherein the ingredients making up the reaction mixturegiving rise to the aluminosilicate gel are employed in such quantitiesas to give said gel, in terms of molar ratios, a composition such thatSi^(IV) :Al^(III) =2 to 20, OH:Al^(III) =0.5 to 8, ST:Al^(III) =0.1 to 4and H₂ O:Al^(III) =40 to
 200. 4. The process according to claim 3,wherein said composition is such that Si^(IV) :Al^(III) =4 to 10, OH⁻:Al^(III) =1 to 6, ST:Al^(III) =0.1 to 1 and H₂ O:Al^(III) =50 to 150.5. The process according to claim 1, wherein the structuring agent STconsists of at least one compound MC chosen from the group consisting ofa) crown ethers whose ring contains 10 to 24 atoms and comprises solelyoxygen atoms as heteroatoms, at least 4 in number, b) compounds derivedfrom the crown ethers defined under a) by partial or completereplacement of the oxygen atoms in the ring by substituents chosen fromsulphur atoms and the groups >NH, >NR and >Si<R_(R) ^(R) in which R is aC₁ -C₄ hydrocarbyl radical, and c) the carbon-containing macropolyringschosen from polyoxadiazabicycloalkanes in which each ring contains 10 to18 atoms and has at least two oxygen atoms in addition to the twonitrogen atoms.
 6. The process according to claim 1, wherein thestructuring agent ST results from the association of at least onecompound MC with a costructurant CS consisting of at least oneoxygen-containing acyclic compound chosen from the compounds of formula

    R.sub.1 --O--C.sub.m H.sub.2m-1 X--O).sub.8 R.sub.2

in which each of R₁ and R₂, which are identical or different, denotes ahydrogen atom or a C₁ -C₄ alkyl radical, X denotes a hydrogen atom or anOH radical, m is equal to 2 or 3 and may be different from one repeatunit to another and g is a number ranging from 1 to
 12. 7. The processaccording to claim 6, wherein the costructurant CS consists of at leastone compound chosen from ethylene glycol methyl ether, ethylene glycoldimethyl ether, ethylene glycol, propylene glycol, polyethylene glycolsof formula HO--CH₂ CH₂ CH₂ O)_(g).sbsb.1 H and their methyl ethers offormula CH₃ O--CH₂ CH₂ O)_(g).sbsb.1 H and polypropylene glycols offormula OH--CH₂ CH₂ CH₂ O)_(g).sbsb.1 H with g₁ denoting a numberranging from 2 to 9 in these formulae.
 8. The process according to claim6, wherein the quantity of structuring agent resulting from theassociation of at least one compound MC and of the costructurant CS,which is present in the reaction mixture intended to form the gel andthe composition of said structuring agent are such as to make the molarratio structuring agent: Al^(III) range from 0.1 to 4 and so as to makethe molar ratio MC:Al^(III) equal to or higher than 0.05.
 9. The processaccording to claim 8, wherein the quantity of structuring agent and itscomposition are such as to make the molar ratio structuring agent:Al^(III) range from 0.2 and 2 and so as to make the molar ratioMC:Al^(III) equal to or higher than 0.1.
 10. The process according toclaim 1, wherein the structuring agent consists of at least one compoundMC₁ chosen from the compounds MC which are macrorings which have 10 to17 atoms in the ring or macropolyrings which have 10 to 18 atoms in eachring, so as to obtain a zeolite which has the faujasite structure ofcubic symmetry.
 11. The process according to claim 6, wherein thestructuring agent results from the association of a costructurant CSwith at least one compound MC₁ chosen from the compounds MC which aremacrorings which have 10 to 17 atoms in the ring or macropolyrings whichhave 10 to 18 atoms in each ring, so as to obtain a zeolite which hasthe faujasite structure of cubic symmetry.
 12. The process according toclaim 1, wherein the structuring agent consists of at least one compoundMC₂ chosen from the compounds MC which are macrorings containing atleast 18 atoms in the ring, so as to obtain a zeolite which has thehexagonal symmetry structure of the hexagonal polytypes of faujasite.13. The process according to claim 1, wherein the source of tetravalentsilicon is chosen from the group consisting of finely divided silicas inthe form of hydrogels, aerogels or colloidal suspensions, water-solublesilicates such as alkali metal silicates like sodium silicate, andhydrolysable silicic esters such as tetraalkyl orthosilicates of formulaSi(OR)₄ in which R denotes a C₁ -C₄ alkyl radical.
 14. The processaccording to claim 1, wherein the source of trivalent aluminum isselected from the group consisting of aluminum salts, aluminum oxidesand hydroxides and aluminates.
 15. The process according to claim 1,wherein the source of hydroxide ions is selected from the group made upof hydroxides of the alkali metals of group IA of the PeriodicClassification of the Elements, the hydroxides of the alkaline-earthmetals Ca, Sr and Ba and quaternary ammonium hydroxides.
 16. The processaccording to claim 1, wherein the reaction mixture contains cationsM^(n+) of at least one metal M, of valency n, other than the metalswhose hydroxides are strong bases, in an overall quantity such as tomake the molar ratio M^(n+) :Al^(III) in said mixture not exceed 0.4.17. The process according to claims 1 to 16, wherein before proceedingto crystallize the gel, crystallization seeds are added to the reactionmixture intended to form said gel, in a quantity ranging from 0.1% to10% by weight of said reaction mixture.
 18. The process according toclaim 1, wherein before proceeding to crystallize the gel, said gel issubjected to a maturing operation, in a closed vessel, at a temperaturebelow the crystallization temperature for a period ranging fromapproximately 6 hours to approximately 6 days.
 19. The process accordingto claim 1, wherein the crystallization of the alumino-silicate gel,with or without seed, is carried out by keeping the said gel at atemperature ranging from 90° C. to 120° C. for a period of between 2hours and fifteen days.
 20. The process according to claim 1, whereinthe calcination of the zeolite precursor is carried out at a temperatureabove 300° C.
 21. Precursors of zeolites of the faujasite structuralclass, consisting of aluminosilicates which have a Si:Al ratio higherthan 1 and which, on the one hand, exhibit a structure of cubic symmetrycomparable with that of faujasite or else a structure of hexagonalsymmetry comparable with that of the hexagonal polytypes of faujasite orelse comprise domains exhibiting a structure of cubic symmetrycomparable to that of faujasite and domains exhibiting a structure ofhexagonal symmetry comparable with that of the hexagonal polytypes offaujasite, and have cavities or channels trapping molecules of astructuring agent, ST, wherein the structuring agent ST consists of atleast one compound MC, chosen from the group consisting ofcarbon-containing macrorings and macropolyrings which contain in therings heteroatoms chosen from O, N, Si and S and which contain 10 to 24atoms per ring, or results from the association of at least one compoundMC with a costructurant CS consisting of at least one oxygen-containingacyclic compound chosen from the compounds of formula R₁ --O--C_(m)H_(2m-1) X--O]₈ R₂, in which each of R₁ and R₂, which are identical ordifferent, denotes a hydrogen atom or a C₁ -C₄ alkyl radical, X denotesa hydrogen atom or an OH radical, m is equal to 2 or 3 and may bedifferent from one repeat unit to the other and g is a number rangingfrom 1 to
 12. 22. Precursors according to claim 21, wherein thecompound(s) MC contained in the structuring agent ST are selected fromthe group consisting of a) crown ethers whose ring contains 10 to 24atoms and comprises solely oxygen atoms as heteroatoms, at least 4 innumber, b) the compounds derived from the crown ethers defined under a)by partial or complete replacement of the oxygen atoms of the ring bysubstituents chosen from sulphur atoms and the groups >NH, >NR and>Si<R_(R) ^(R), in which R is a C₁ -C₄ hydrocarbyl radical, and c) thecarbon-containing macropolyrings chosen from polyoxadiazabicycloalkanesin which each ring contains 10 to 18 atoms and has at least two oxygenatoms in addition to the two nitrogen atoms.
 23. Precursors according toclaim 21, wherein in addition to the compound(s) MC, the structuringagent ST also contains a costructurant CS consisting of at least oncompound chosen from ethylene glycol methyl ether, ethylene glycoldimethyl ether, ethylene glycol, propylene glycol, polyethylene glycolsof formula HO--CH₂ CH₂ O)_(g).sbsb.1 H and their methyl ethers offormula CH₃ --O--CH₂ CH₂ O)_(g) ₁ H and propylene glycols of formulaHO--CH₂ CH₂ CH₂ O)_(g).sbsb.1 H with g₁ denoting a number ranging from 2to 9 in these formulae.
 24. The process of claim 1 wherein the Si:Alratio is greater than
 3. 25. The process according to claim 14, whereinthe source of trivalent aluminium is selected from the group consistingof alkali metal aluminates and aluminium trialkoxides of formula Al(OR)₃in which R is C₁ -C₄ alkyl radical.
 26. The process according to claim16, wherein said cations M^(nt) are selected from the group consistingof Co⁺⁺, Cd⁺⁺, Mg⁺⁺ and Ag⁺.
 27. The process according to claim 17wherein the recrystallization seeds are produced by grinding a zeoliteof the same kind as the crystalline phase to be produced or by synthesisfrom a suitable nucleating solution.
 28. Precursors according to claim21 exhibiting a structure of cubic symmetry comparable with that offaujasite, wherein they exhibit an x-ray diffraction pattern comparablewith that defined in Table III

                  TABLE III                                                       ______________________________________                                        2θ (°)                                                                   d.sub.hkl (10.sup.-1 nM)                                                                        (h k l) I/Io                                        ______________________________________                                         6.26   14.10      ± 0.2   (1 1 0)                                                                             VS                                        10.23   8.65                  (2 2 0)                                                                             w                                         12.01   7.35                  (3 1 1)                                                                             mS                                        15.77   5.615      ± 0.05  (3 3 1)                                                                             S                                         18.81   4.713                 (5 1 1)                                                                             m                                         20.49   4.331                 (4 4 0)                                                                             mS                                        22.93   3.875                 (6 2 0)                                                                             w                                         23.77   3.740                 (5 3 3)                                                                             mS                                        25.15   3.537                 (4 4 4)                                                                             vw                                        25.93   3.433                 (5 5 1)                                                                             vw                                        27.19   3.276                 (6 4 2)                                                                             mS                                        27.93   3.191      ± 0.008 (7 3 1)                                                                             vw                                        29.81   2.994                 (7 3 3)                                                                             w                                         ______________________________________                                    

and are represented by a formula which, reduced to a unit cell of thecubic structure, is written

    (vM.sub.1.sup.qt) (wM.sup.nt) ((SiO.sub.2).sub.192-x (AlO.sub.2).sub.x).sup.x- (PST.sub.1) (zH.sub.2 O)

and in which M1^(qt) denotes a q-valent cation of a metal selected fromthe group consisting of group IA of the Periodic Classification of theElements (q=1), an alkaline-earth metal chosen from Ca, Sr and Ba (q=2),and a monovalent cation containing nitrogen (q=1) M^(n+) denotes acation of a metal M of valency n other than a cation M1^(qt), x, z, vand w are numbers such that 30≦x≦96, z≧0 and depending on the hydrationstate of the precursor, 0<v≦x/q and 0≦w≦x/n with qv+wn≧x, p is a numbersuch that 4≦p≦10 and ST₁ denotes at least one compound MC₁ selected fromthe compounds MC consisting of macrorings containing from 10 to 17 atomsin the ring or macropolyrings containing 10 to 18 atoms in each ring ora mixture of at least one compound MC₁ and of the constructurant CS. 29.Precursors according to claim 21, exhibiting a structure of hexagonalsymmetry comparable with that of the hexagonal polytypes of faujasite,wherein they exhibit an x-ray diffraction pattern comparable with thatgiven in Table IV below:

                  TABLE IV                                                        ______________________________________                                        2θ (°)                                                                    d.sub.hkl (10.sup.-1 nM)                                                                      (h k l) I/Io                                         ______________________________________                                         5.88    15.02     ± 0.2  (1 0 0)                                                                             VS                                          6.24    14.15               (0 0 2)                                                                             S                                           6.65    13.28               (1 0 1)                                                                             S                                          10.12    8.73      ± 0.08 (1    )                                                                             w                                          11.01    8.03                (1 0 3)                                                                             mw                                         11.93    7.41                (1 1 2)                                                                             mS                                         13.58    6.515               (2 0 2)                                                                             vw                                         15.57    5.686     ± 0.05 (0 0 5)                                                                             mS                                         15.86    5.580               (2 1 1)                                                                             mw                                         16.70    5.305               (1 0 5)                                                                             mw                                         17.15    5.165               (2 0 4)                                                                             S                                          18.16    4.88                (2 1 3)                                                                             mw                                         18.71    4.74                (1 1 5)                                                                             mw                                         19.65    4.509               (1 0 6)                                                                             mS                                         20.42    4.345               (2 2 0)                                                                             S                                          22.14    4.011               (3 1 2)                                                                             mS                                         22.71    3.912               (1 0 7)                                                                             mw                                         23.32    3.811               (3 1 3)                                                                             mw                                         23.60    3.766               (3 0 5)                                                                             mw                                         24.68    3.604               (3 1 4)                                                                             mw                                         25.81    3.449               (2 2 5)                                                                             w                                          26.49    3.362               (2 1 5)                                                                             w                                          ______________________________________                                    

and are represented by a formula which, reduced to a hexagonal unit cellof the crystalline structure, is written (u M1^(qt)) (rM^(n+))

    (SiO.sub.2).sub.96-y (AlO.sub.2).sub.y).sub.y- (j ST.sub.2) (t H.sub.2 O)

with, in this formula, M₁ ^(qt) denoting a q-valent cation of a metalselected from the group consisting of IA of the Periodic Classificationof the Elements (q=1), an alkaline-earth metal chosen from Ca, Sr and Ba(q=2) and a monovalent cation containing nitrogen (q=1) M^(nt) denotinga cation of a metal M of valency n other than a cation M₁ ^(qt), y, u, rand t being numbers such that 15≦y≦48, t≧0 and depending on thehydration state of the precursor, 0<u≦y/q and 0≦r≦y/n with q u+n r≧y, jbeing a number such that 2≦j≦5 and ST₂ denoting at least one compoundMC₂ chosen from the compounds MC which are macrorings containing atleast 18 atoms in the ring.
 30. A process for the preparation ofzeolites which have the cubic symmetry structure of faujasite bycalcination of the precursors of claim 38, the zeolites obtained havinga cubic unit cell parameter value of between 2.4 and 2.5 nm, exhibitingan x-ray diffraction pattern comparable with that given in Table Ibelow:

                  TABLE 1                                                         ______________________________________                                        2θ (°)                                                                   d.sub.hkl (10.sup.-1 nM)                                                                        (hkl)   I/Io                                        ______________________________________                                         6.245  14.14      ± 0.2   (1 1 1)                                                                             VS                                        10.205  8.66                  (2 2 0)                                                                             S                                         11.965  7.39                  (3 1 1)                                                                             mS                                        15.735  5.627      ± 0.05  (3 3 1)                                                                             S                                         18.775  4.721                 (5 1 1)                                                                             w                                         20.465  4.335                 (4 4 0)                                                                             mw                                        22.895  3.881                 (6 2 0)                                                                             w                                         23.755  3.727                 (5 3 3)                                                                             mS                                        25.105  3.544                 (4 4 4)                                                                             vw                                        25.965  3.428                 (5 5 1)                                                                             vw                                        27.175  3.279                 (6 4 2)                                                                             mS                                        27.885  3.196      ± 0.008 (7 3 1)                                                                             vw                                        29.765  2.999                 (7 3 3)                                                                             w                                         ______________________________________                                    

and corresponding to the formula which, reduced to unit cell of thecubic structure, is written

    (v M.sub.1.sup.q+) (w M.sup.n+) ((SiO.sub.2).sub.192-x (AlO.sub.2).sub.x).sup.x- (z H.sub.2 O)

and in which, M₁ ^(qt), M^(nt), x,z,v and w have the meanings given inclaim
 37. 31. A process for the preparation of zeolites which have thehexagonal symmetry structure of the hexagonal polytypes of faujasite bycalcination of the precursors of claim 29, the zeolites obtained havinghexagonal unit cell parameters a,b,c, of the said structure such that1.72 nm<a=b<1.77 nm and 2.80 nm<c<2.89 nm, exhibiting an x-raydiffraction pattern comparable with that given in Table II

    ______________________________________                                        2θ (°)                                                                   d.sub.hkl (10.sup.-1 nM)                                                                        (h k l) I/Io                                        ______________________________________                                         5.88   15.03      ± 0.2   (1 0 0)                                                                             VS                                         6.23   14.2                  (0 0 2)                                                                             VS                                         6.66   13.3                  (1 0 1)                                                                             S                                          8.40   10.52                 (1 0 2)                                                                             w                                         10.19   8.68       ± 0.08  (1 1 0)                                                                             S                                         11.06   7.99                  (1 0 3)                                                                             mS                                        11.78   7.51                  (2 0 0)                                                                             mS                                        11.95   7.40                  (1 1 2)                                                                             mS                                        13.49   6.56                  (2 0 2)                                                                             vw                                        15.06   5.88       ± 0.05  (2 0 3)                                                                             w                                         15.58   5.68                  (0 0 5)                                                                             S                                         15.89   5.57                  (2 1 1)                                                                             w                                         16.73   5.29                  (1 0 5)                                                                             w                                         17.18   5.16                  (2 0 4)                                                                             S                                         18.22   4.87                  (2 1 3)                                                                             w                                         18.79   4.72                  (1 1 5)                                                                             w                                         19.67   4.51                  (1 0 6)                                                                             w                                         20.45   4.34                  (2 2 0)                                                                             mS                                        22.22   4.00                  (3 1 2)                                                                             w                                         22.75   3.91                  (1 0 7)                                                                             w                                         23.30   3.82                  (3 1 3)                                                                             w                                         23.66   3.76                  (3 0 5)                                                                             S                                         24.75   3.59                  (3 1 4)                                                                             w                                         25.83   3.45                  (2 2 5)                                                                             w                                         26.52   3.36                  (2 1 5)                                                                             w                                         27.16   3.28                  (4 1 0)                                                                             w                                         28.77   3.103      ± 0.008 (3 2 4)                                                                             w                                         30.38   2.942                 (4 0 6)                                                                             vw                                        30.89   2.894                 (3 3 0)                                                                             w                                         31.20   2.866                 (5 0 3)                                                                             w                                         31.56   2.834                 (3 3 2)                                                                             vw                                        ______________________________________                                    

and corresponding to a formula which, reduced to a unit cell of thehexagonal structure, is written

    (u M.sub.1.sup.q+) (r M.sup.n+) ((SiO.sub.2).sub.96-y (AlO.sub.2).sub.y).sup.y- (t H.sub.2 O)

and in which the symbols M₁ ^(qt), M^(nt), y,t,u and r have the meaningsgiven in claim
 38. 32. A process for the preparation of precursors ofzeolites belonging to the faujasite structural class and exhibiting aSi:Al ratio higher than 1, said process comprising first forming areaction mixture which has a small pH higher than 10 and contains water,a source of tetravalent silicon, a source of trivalent aluminum, asource of hydroxide ions in the form of a strong inorganic or organicbase and a structuring agent ST so as to produce an alumino silicate gelhaving the composition to permit its crystallization into a compound ofthe faujasite structural class, and the gel obtained is then kept at atemperature not exceeding 150° C. and under a pressure at least equal tothe autogenous pressure of said gel for a sufficient period to effectcrystallization of the gel into a precursor of the zeolite consisting ofthe zeolite with the structuring agent ST trapped in its cavities andconsisting of at least one compound MC selected from the groupconsisting of the carbon-containing macrorings and macropolyrings whichcontain in the rings heteroatoms selected from the group consisting ofoxygen, nitrogen, silicon and sulfur, and which contain 10 to 24 atomsper ring.
 33. The process according to claim 32, wherein the quantity ofstructuring agent ST in the reaction mixture intended to form the gel issuch as to make the molar ratio ST:Al^(III) ranging from 0.1 to
 4. 34.The process according to claim 32, wherein the ingredients making up thereaction mixture giving rise to the aluminosilicate gel are employed insuch quantities as to give said gel, in terms of molar ratios, acomposition such that SI^(IV) :Al^(III) ^(III) =2 to 20, OH⁻ :Al^(III)=0.5 to 8, ST:Al^(III) -0.1 to 4 and H₂ O:Al^(III) =40 to
 200. 35. Theprocess according to claim 32, wherein the structuring agent ST consistsof at least one compound MC chosen from the group consisting of a) crownethers whose ring contains 10 to 24 atoms and comprises solely oxygenatoms as heteroatoms, at least 4 in number, b) compounds derived fromthe crown ethers defined under 1) by partial or complete replacement ofthe oxygen atoms in the ring by substituents chosen from sulphur atomsand the groups >NH, >NK and SI<_(R) ^(R) in which R is a C₁ -C₄hydrocarbyl radical, and c) the carbon-containing macropolyrings chosenfrom polyoxadiazabicycloalkanes in which each ring contains 10 to 18atoms and has at least two oxygen atoms in addition to the two nitrogenatoms.
 36. The process according to claim 32, wherein the structuringagent ST results from the association of at least one compound MC with acostructurant CS consisting of at least one oxygen-containing acycliccompound chosen from the compound of the formula

    R.sub.1 --O--C.sub.m H.sub.2m-1 X--O).sub.g R.sub.2

in which each of R₁ and R₂, which are identical or different, denotes ahydrogen atom or a C₁ -C₄ alkyl radical, X denotes a hydrogen atom or anOH radical, m is equal to 2 or 3 and may be different from one repeatunit to another and g is a number ranging from 1 to
 12. 37. The processaccording to claim 36, wherein the quantity of structuring agentresulting from the association of at least one compound MC and of thecostructurant CS, which is present in the reaction mixture intended toform the gel and the composition of the said structuring agent are suchto make the molar ratio structuring agent:Al^(III) range from 0.1 to 4and so as to make the molar ratio MC:Al^(III) equal to or higher than0.05.
 38. The process according to claim 32, wherein the structuringagent consists of at least one compound MC 1 chosen from the compoundsMC which are macrorings which have 10 to 17 atoms in the ring ormacropolyrings which have 10 to 18 atoms in each ring, so as to obtain azeolite precursor which has the faujasite structure of cubic symmetry.39. The process according to claim 36, wherein the structuring agentresults from the association of a costructurant CS with at least onecompound MC₁ chosen from the compounds MC which are macropolyrings whichhave 10 to 17 atoms in the ring or macropolyrings which have 10 to 18atoms in each ring, so as to obtain a zeolite precursor which has thefaujasite structure of cubic symmetry.
 40. The process according toclaim 32, wherein the structuring agent consists of at least onecompound MC₂ chosen from the compound MC which are macrorings containingat least 18 atoms in the ring, so as to obtain a zeolite precursor whichhas the hexagonal symmetry structure of the hexagonal polytypes offaujasite.
 41. The process according to claim 32, wherein the source oftetravalent silicon is chosen from the group consisting of finelydivided silicas in the form of hydrogels, aerogels or colloidalsuspensions, water-soluble silicates such as alkali metal silicates andhydrolysable silicic esters such as tetraalkyl orthosilicates of formulaSi(OR)₄ in which R denotes a C₁ -C₄ alkyl radical.
 42. The processaccording to claim 41, wherein the source of trivalent aluminum ischosen from the group consisting of aluminium salts, aluminium oxidesand hydroxides, aluminates and aluminium esters.
 43. The processaccording to claim 32, wherein the source of hydroxide ions is chosenfrom the group consisting of hydroxides of the alkali metals of group IAof the Periodic Classification of the Elements, the hydroxides of thealkaline-earth metals Ca,Sr and Ba and quaternary ammonium hydroxides.44. The process according to claim 32, wherein the reaction mixturecontains cations M^(n+) of at least one metal M, of valency n, otherthan the metals whose hydroxides are strong bases, in an overallquantity such as to make the molar ratio M^(n+) :Al^(III) in saidmixture not exceed 0.4.
 45. The process according to claim 32, whereinbefore proceeding to crystallize the gel, crystallization seeds areadded to the reaction mixture intended to form said gel, in a quantityranging from 0.1% to 10% by weight of said reaction mixture.
 46. Theprocess according to claim 32, wherein before proceeding to crystallizethe gel, said gel is subjected to a maturing operation, in a closedvessel, at a temperature below the crystallization temperature for aperiod ranging from approximately 6 hours to approximately 6 days. 47.The process according to claim 32, wherein the crystallization of thealuminosilicate gel, with or without seed, is carried out by keepingsaid gel at a temperature ranging from 90° C. to 120° C. for a period ofbetween 2 hours and fifteen days.